Cardiovascular disease, including atherosclerosis, is the leading cause of death in the U.S. A number of methods and devices for treating coronary heart disease have been developed, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary arterial narrowing.
One method for treating atherosclerosis and other forms of coronary narrowing is percutaneous transluminal coronary angioplasty, hereinafter referred to as “angioplasty” or “PTCA”. The objective in angioplasty is to enlarge the lumen of the affected coronary artery by radial expansion. This is generally accomplished by inflating a balloon within the narrowed lumen of the affected artery. The wall of the artery itself may also be stretched as the balloon is inflated. With simple angioplasty, the balloon is threaded through the artery with a catheter and inflated at the place where the blood vessel is blocked. After the procedure, the balloon is then removed. With simply angioplasty alone, arteries may close up again or re-narrow. This narrowing is known as restenosis.
To reduce the risk of restenosis, a stent may also be inserted during angioplasty. A stent is a tube, often made of metals or occasionally plastic materials that is inserted into a vessel or a passage in the body to keep the lumen of the vessel open and to prevent closure due to a stricture or external compression. The use of a stent may reduce the risk of restenosis. However, stent insertion can cause undesirable reactions such as inflammation, infection, thrombosis, or proliferation of cell growth that occludes the passageway.
Restenosis occurs because the blood vessel wall is injured when the stent is implanted. The area then becomes inflated and new cells form scar tissue. The arterial walls may become so thick in some instances that they sometimes protrude into the mesh of the stent. In such cases, a further angioplasty may be undergone, and a new stent may be placed inside the existing one. If restenosis continues, the eventual alternative may be bypass surgery.
Alternatively, a treated stent may be inserted during the angioplasty. Such a treated stent may eliminate the need for repeat angioplasties and could spare some patients the trauma, risk and prolonged recovery associated with heart bypass surgery. The treated stent contains a therapeutic agent to assist in preventing restenosis. The stent is bioengineered to release doses of the therapeutic agent which may or may not be contained in a coating on the stent. Agents contemplated act to stop new cells from forming without impairing the healing of the vessel. Agents may also dampen inflammation and have antibiotic properties.
However, because the treated stent may contain a therapeutic drug, treated stents present problems associated with drug administration. For example, for a drug to be administered effectively, the integrity of the drug's effective dosage should be maintained. Certain drugs require regulated conditions for efficacy, such as regulated air circulation or lack thereof, regulated exposure to light and oxygen.
Prior art packaging systems for treated stents have typically comprised a thermoform tray insert in a foil pouch, or a thermoform tray having a TYVEK® material lid in a foil pouch, into which the stent is vacuum packed. Such conventional packaging for stents do not provide for regulation of ambient conditions such as circulation of air or exposure to light and oxygen. Without such appropriate regulation, the efficacy of the drug and/or drug coating may be reduced. Moreover, these packages tend to be heavier than those of the present invention, they utilise more material and they require more operator handling time to pack and so are more labour intensive to produce. TYVEK® material is commercially available from DuPont and consists of multiple spun woven extruded polyethylene strands, compressed under high pressure to form a complex system of microscopic porous channels which provides a tortuous path within a thin flexible opaque sheet.